1. Field of the Invention
The present invention relates to beam switching antennae, and more particularly, to a beam switching antenna system and a method and apparatus for controlling the same, by which optimal antenna characteristics can be maintained according to a peripheral environment, the necessary time and power consumption of searching an optimal beam-direction can be reduced, and electromagnetic waves of a beam emanating from an antenna toward the user's head can be minimized.
2. Discussion of the Related Art
Antenna configurations include a Yagi-type, parabolic, helical, planar, and the like, with beam patterns which may be classified as directional or omni-directional. A contemporary mobile communication system uses an omni-directional antenna. An omni-directional antenna according to a related art is shown in FIG. 1.
Referring to FIG. 1, an omni-directional antenna includes a monopole element 11, which is a quarter wavelength (λ/4) element perpendicularly disposed with respect to a surface of a conductive reflector 13 having a typically horizontal orientation. The monopole element 11 is connected to a power feed line 12 via a power feed connector (not shown), and the conductive reflector 13 is grounded via a ground line 14 establishing a reference voltage. The monopole element 11 converts radio frequency energy from the power feed line 12 to a transmitting electromagnetic wave (beam pattern) radiating in the atmosphere with a predetermined pattern and converts an electromagnetic wave received from the atmosphere to an electrical signal feeding the power feed line 12. The received signal is the forward link in a mobile communication system, and the transmitted signal is the reverse link.
An inherent characteristic of the above omni-directional antenna is that its beam pattern is non-directional and thus cannot be adapted to a peripheral environment or usage condition, which may call for a directional beam pattern. That is, the transmission energy radiating in a specific direction should in many cases be greater than or less than that radiating in another direction, but the omni-directional antenna of the related art produces a beam pattern in which the transmitted energy levels are roughly equal in all directions, which poses several disadvantages.
For example, the power required to transmit a given distance using an omni-directional antenna is greater than the power required if an antenna transmitting a directional beam were employed. Reverse-link transmission at greater power levels produces a variety of negative effects, including reduced data through rates, increased error rates, and a lowered forward-link communication capacity per cell. In addition, some end users are concerned with electromagnetic waves emanating from an antenna held close to the head, as in the case of a hand-held mobile communication terminal. Accordingly, the use of an omni-directional antenna in such cases inherently causes raised concerns. Moreover, the length of the antenna adopted by a mobile communication terminal, such as a cellular telephone, is desirably short to facilitate miniaturization while maintaining an aesthetically pleasing exterior, and the operating band of the mobile communication terminal is fixed such that the λ/4 length of the omni-directional antenna cannot be shortened. Therefore, the omni-directional antenna of the related art inhibits miniaturization or necessitates an externally mounted antenna.
Meanwhile, an adaptive directional antenna such as that proposed in U.S. Pat. No. 6,100,843 enables the orientation of the beam pattern in a specific direction as desired. The proposed antenna uses a complex configuration of five antenna elements, comprising four antenna elements disposed at the four corners of a square base having a centrally disposed fifth antenna element, and control circuitry including a phase shifter for controlling the phase of a transmission/reception signal of each antenna element using a time-consuming set of operations, during which time a “call disconnect” condition may occur. As such, the adaptive directional antenna is too large, too costly, and too slow and is thus impractical for a mobile communication terminal.
In the operation of the above adaptive directional antenna, an imaginary circle is drawn around the mobile communication terminal and divided into a plurality of angles, and each angle is searched to determine the optimum beam direction. During an idle time, a beam direction is determined for each antenna element through an execution of a loop of operations for each angle for each antenna element. Each loop includes steps of measuring the pilot signal, storing the measurement information, and setting an optimal phase. The imaginary circle may comprise as many as 360 angles, with a greater number imparting greater accuracy but necessitating an even longer time for completing the loop operations. The reverse link power must be boosted throughout the search operation for determining the optimal beam direction, which increases power consumption and produces the same negative effects of an omni-directional antenna.